NP231 fluid replacement/additives

[coolwind57]

I paid a local shop to put in an axle seal, which required new bearings as part of the job for my D44.  Less than a week later, I was hearing some concerning noise and naturally I thought they screwed up the bearings install.  Turns out, the noise was coming from my NP231 transfer case.  Less than a year ago, I had installed a new rear seal on it and I now wonder if I had indeed topped the 231 off afterwards.

 

The shop checked the fluid level and it was about a quart low.  They topped off and the noise almost immediately went away.

 

After driving for a few days and with the windows down, I can faintly hear that same noise, although just barely this time.  I was thinking of dropping the fluid, and adding all new with maybe a kiss of some kind of additive, maybe a Lucas product or something.  Just to maybe give a bit more protection and further prevent noise.

 

You guys got any recommendations on NP231 fluids/additives?     

[87MJTIM]

I believe the NP231 takes ATF.  I don't know what grade, though.

[coolwind57]

2 minutes ago, 87MJTIM said:

I believe the NP231 takes ATF.  I don't know what grade, though.

yea, the shop topped off with ATF+4 if I remember correctly.  Curious what others are using, especially for added performance.  

[75sv1]

14 minutes ago, coolwind57 said:

yea, the shop topped off with ATF+4 if I remember correctly.  Curious what others are using, especially for added performance.  

I ran some type of synthetic transmission fluid. AMSOIL but I think it was for a Ford FMX. I think ATF+4 is a synthetic. The factory fill is DexIII/Mercon I think. They do make some synthetics for that. 

[1stDeuce]

I run 50/50 Valvoline Maxlife atf and supertech 80w90 in all my chain t-cases. Synthetic 90wt is about the viscosity of 30wt oil (different scale) and seems to quiet loose cases a bit compared to using just ATF, which is 5 to 10wt.



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[ghetdjc320]

Run 30wt motor oil in it. Seriously, works great. 

[Tex06]

11 hours ago, ghetdjc320 said:

Run 30wt motor oil in it. Seriously, works great. 

I can't speak on the transfer case for this but I know a lot of folks recommend synthetic motor oil in the AX-15. I did this 2x and both times I recorded case temperatures 20-40 deg F higher than with gear oil. As a hydraulics engineer who deals with fluids and lubricants daily....motor oil isn't great for lubricating gears or being under high pressure. It also tends to breakdown faster due to the additives in it (hence why most manufacturers recommend an oil change every 6 months, regardless of mileage).

Dextron III/IV is cheap, that's what I use in mine. Make sure it's topped up and flush every 30k miles if you're concerned. Most additives are just a heavier weight synthetic oil with "proprietary ingredients" added which adds negligible protection at best, can cause extra damage at worse.  I've seen where the additive in the main oil (all oil products are some type of "base oil" with additives to make it Shell, Chevron, Pennzoil, etc.) will react with whatever the additive in the "additive product" is and produce gunk or sludge which blocks ports and passages. Not as big a deal in a transfer case as an auto tranny or a motor with an oil pump, but I'm not a big fan of throwing money away on something of questionable value.

[Eagle]

https://www.mrmoly.com/product-p/55932.htm